The present invention relates to fly-height testing in storage devices. In particular, the present invention relates to interferometer fly-height testing.
In many storage devices, a slider containing a read or write head flies above a moving medium, such as a disc, in order to read or write data to various parts of the medium. The fly-height of the slider, he distance between the slider""s bottom surface and the surface of the medium, affects the head""s ability to read and write data to the medium. To ensure that the fly-height of a slider is within specifications, the slider is tested using a fly-height tester before it is placed in a drive.
Most fly-height testers determine the distance between the slider and a test medium using a technique known as interferometry. Under this technique, a beam of light is passed through the medium and onto the slider as the slider flies over the medium. This causes the light to be reflected twice, once at the surface of the medium and once at the slider. These two reflective beams interfere with each other such that some wavelengths of light have a high amplitude in the combined reflected light while other wavelengths of light have zero amplitude. By measuring the intensity of the light at particular wavelengths, it is possible to determine the distance between the slider and the disc surface.
Because the distance measurement is dependent on the amplitude of the reflected light, any noise that affects the amplitude of the reflected light will affect the accuracy of the measurement. In prior art systems, one major source of optic noise has been the light source used to generate the light beam. For example, some testers use arc lamps that produce a noisy light beam due to the manner in which they generate light. Other fly-height testers use lasers that generate a light that is initially relatively clean but that is prone to speckling when it reflects off a surface.
Arc lamps and lasers are also undesirable because they are inefficient and produce a large amount of heat. This adds to the cost of the tester because the tester must be designed to vent the heat.
The present invention provides a solution to this and other problems and offers other advantages over the prior art.
A method and fly-height tester include a moving medium land a slider mount that holds a slider in proximity with the medium so that the slider flies relative to the medium. At least one light emitting diode generates a light that is directed by optics so that it reflects off the medium and the slider. The reflected light is directed by second optics to at least one detector, where each detector is capable of generating an electrical signal based on the amplitude of at least one wavelength of light in the reflected light. A distance calculator then determines the distance from the slider to the medium based on the at least one electrical signal.